In an apparatus driven by an electric motor, misalignment between rotating components thereof and the electric motor or stack-up of tolerance in bearing clearance may cause undesired results including vibration, noise, or damage to the motor or apparatus. Additionally, reaction moments caused by driving the shaft may cause undesirable vibration or unexpected internal interference within the motor. For example, electric motors may “cog” causing excessive noise and jerkiness if the stator undergoes undesirable rotational vibration.
As an example, a drawworks is a common piece of oil field equipment that is used in oil and gas drilling and production. A drawworks is positioned to lift and lower a travelling block in a drilling rig. The travelling block is suspended by a hoisting line, also known as a drill line, drilling line, or “drilline”, from the derrick of the drilling rig, and is typically used to raise and lower drill string and casing out of and into a wellbore. The hoisting line is coupled to a drum which is rotated by the rotor. Typically, at least one motor is mounted on a surface, such as a skid, platform, or directly to the drill floor. Any misalignment between the rotor of the motor and the shaft of the drum or any bearing clearance may cause undesired vibration or damage to the drawworks. In order to account for any misalignment, the motor may be coupled with a flexible coupler to the drum. However, a flexible coupler may not be as strong as a solid shaft, and may serve to limit the maximum power capable of being used by the drawworks. Additionally, a flexible coupler will add length and complexity to the drawworks when compared to a stiff coupling. Fixedly mounting the motor to the surface may exacerbate any misalignment between the rotor and the shaft, as well as allow undesired rotational vibration of the stator. Any movement that is the result of a misalignment or bearing clearance may be suppressed by the fixed mounting to the surface, which may cause stresses in the shaft, bearing, and surface mounts, which may lead to premature fatigue and possibly failure.